Displaceable plunger mercury switch



Dec. 15, 1964 D. J. ANDERSON DISPLACEA'BLE PLUNGER" MERCURY SWITCH 2 Sheets-Sheet 1 Filed April 16, 1962 INVENTOR I DONALD J4Y4A7DRJON Dec. 15,- 1964 'n. J. ANDERSON DISPLACEABLE PLUNGER MERCURY smca 2 Sheets-Sheet 2 Filed April 16, 1962 ORNEYS United States Patent "ice 3,161,745 DlSPLACEABLE PLUNGER MERCURY SWliT'CH Donald lay Anderson, Haddcniield, NJ. (74 Harestene Hill, Cathcrharn, Surrey, England) Filed Apr. 16, 1962, Ser. No. 187,853 ll Qlaims. ((Jl. 200-4112) switch adaptablepermissibly to heavy currents and also I suitable for high frequency which will be extremely com act.

p A further purpose is to obtain a low cost switch which will give reliable service under heavy current and high frequency service, as well as under low currents and normal frequencies.

A further purpose is to operate an electric switch on heavy currents and suitably on high frequency with low heat loss. v

A further purpose is to equalize skin effects in high frequency switching. t

A further purpose is to produce an electric switch which can be employed in either make or break contact service with low maintenance.

A further purpose is to provide an electric switch which is totally sealed and therefore free from contamination, and which can suitably operate in a vacuum or in an inert atmosphere and therefore be free from oxidation and other objectionable corrosion effects.

A further purpose is to provide an electric switch which can operate at heavy currents and suitably also at high frequency, but will be capable of functioning under low control power consumption.

Further purposes appear in the specification and in. the claims.

In the drawings 1 have chosen to illustrate one only of the numerous embodiments in which the invention may appear, with a variation suitable for A.C. control power, the form shown. in the variation being chosen from the standpoint of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

FiGURE 1 is an axial elevation of the switch of the invention showing the switch in an off position taken on the line llll of FIGURE 2.

FIGURE 2 is a horizontal section taken on line 2-2 of FIGURE 1;

FIGURE 3 is' a view similar to FIGURE 1 showing the switch in an on position.

FIGURE 4 is a fragmentary section similar to FIG- URES 1 and 3 showing the switch under an excess load and the mercury divided.

FIGURE 5 is a sectional View of the plunger.

FIGURE 6 is a plan view of a modified plunger of the invention.

While the switch of the invention is applicable for making or breaking electric circuits either of AC. or DC, and using either AC. or DC. control. power, it is believed to have its widest application in the making or breaking of circuits carrying relatively heavy currents up to the order or" 1200 amperes or greater, and especially where the current carrying function is complicated by the presence of high frequency. When high frequency is referred to, it is normally intended to designate frequencies in the 3,161,745 Patented Dec. 1 5, 1 964,

range above normal 60 cycles commercial frequency and up to the order of 20,000 cycles persecond.

I Vlhile the switch of the invention has adequate capacity for making or breaking circuits under load, it is primarily intended for switching which is accomplished when the circuit is not under load.

Considering first a typical high frequency and high current application, the invention is especially suited to switching capacitors in or out of the circuit in an electric induction high frequency furnace, suitably of the coreless type.

in such circuits, it will be evident that a change either in the electrical properties, quantity or composition of the charge will change the inductance of the secondary and therefore change the required capacitance in the primary circuit in order to correct the power factor to obtain a load close to unity.

In the prior art, contacts of the mechanical type have been used. There has been diiiiculty through arcing and pitting, through the presence of tracking on account of dirt in the atmosphere, through freezing of contacts which have prevented the breaking of the circuit, and also because the switching has been bulky, space consuming, and has required considerable power to operate.

By the present invention, these diiilculties are overcome in large measure. Most of the mechanical contact devices previously used are four to five times the size of the switching device of the present invention. The device of the present invention is also very economical to produce, costing of the order of one quarter as much as competitive mechanical contact devices.

The device of the present invention lends itself particularly well to water cooling, so that very effective elimination of heat can be obtained, while at the same time the heat losses are low. I

'l. he present invention makes contact through a relatively thin tubular portion or annulus of mercury, thus making very etlective use of the quantity of mercury from the standpoint of skin effect. Furthermore, the terminals are themselves thin annuli and also highly efltective from the standpoint of skin effect. As' a further aspect, the lead-ins to the terminals are at opposite positions with respect to the terminals so as to effectively equalize the skin eliect distribution over the contact area.

An important aspect of the invention is that the device is capable of functioning notwithstanding that gross overloads of current occur for short periods of time. For this purpose, an electrically conducting plunger which displaces the mercury into contact between the terminals leaves a throttling space into which mercury is repelled when the magneto motive force of the great overload tends to makke the mercury exert abnormal, and almost excessive, hydraulic pressure. The displacing plunger itself occupies a position across the terminals and continues to carry current even when the magneto motive force is great enough to separate the mercury located betwee the two terminals.

' The switch ofthe invention is capable of being maintained in a sealed space, where it will very efiectively prevent corrosion, permissibly employing from a vacuum to an inert atmosphere such as argon.

The sealed aspect also prevents the intrusion of dust or water which is very likely to be present in the atmosphere of a factory, so that there can be no danger of tracking through deposits on the terminals or on the switching element, or tracking on the insulation between the terminals.

The device of the invention can be operated with very low control power either of AC. or DC.

The device of the invention, in case of loss of control power, either through interruption of its power source or other failure of some component in the control circuit,

is desirably made to automatically close the circuit, and thus create an overload for which protection can be provided, as by protective relaying as well known. Thus the device of the invention can in elfect be made to fail safe.

Considering first the device as shown in FIGURES 1 to 5, I there illustrate a tubular switch terminal 2 3, united as by welding or brazing to a terminal lug 21 which has an arm 22 sealing the bottom of the tubular terminalZtl and a transverse arm 23, in this case upstanding, which can be secured as by bolting through holes 24 to a suitable bus bar desirably of the water cooled variety commonly used in induction furnaces. If the bus bar has sulficient heat absorbing capacity it need not be water cooled.

Coaxial to the tubular terminal 29, and above it, is placed as tubular terminal'25, of the same interior diameter as the tubular terminal and separated from it by the switch open gap 26. The terminal 25 extends through an opening in switch terminal lug '27 and is united to the switch terminal lug 27 as by brazing or welding at 28. The switch terminal lug has one arm 34? which is parallel to the lower arm 22 of the opposite terminal and has a depending arm 31 which can suitably be connected to the device to be switched, which in a particular case may be a capacitor.

The upper terminal 25 is desirably extended up through the opening 32 in the lug arm 30, and can suitably make connection to a metallic or non-metallic tube 33 as by a telescoping fit at 34. The tube 33 has a top 33' to form an inverted closed cylinder.

The switch terminals 20 and 25 of solid metal current carrying components are preferably made or" high conductivity copper, which will assure minimum RI? loss and will amalgamate with mercury forming a low resistance surface layer, while the remainder of the terminal resists further attack. If desired, all copper components in direct contact with mercury may be coated with a metallic coating which will not wet or amalgmate with mercury but will still form a low resistance contact. This could be molybdenum or tungsten sprayed onto the copper as with a plasma gun.

In order to provide a non-tracking insulator across the terminal gap, I surround the switch terminals 2t? and 25 with a tube of high temperature ceramic 35 suitably of the type which is capable or functioning in circuit breaker insulator applications exposed to the air. For example, any material suitable of functioning as a ceramic in an arc chute of a circuit breaker is satisfactory. The tube 35 is joined by cementing as by expoxy resin at 36, 37, 3d and 40.

Thus, a bottom container is formed by arm 22 of lug 21 at the bottom, terminal 29 at the lower side, then ceramic tube 35, then tubular terminal 25. Above this point ceramic tube 41 is cemented as at 42 to the in. .de of the tubular terminal 25 and the upward extending tube 33 and the top 33 is suitably covered by epoxy resin at 43'.

In assembling the device, a mercury charge 44 is placed in the terminal 26} when the switch is open which will completely fill the bottom cup portion formed by the terminal.

A magnetically susceptible core or plunger 45 fills the upper space when the surrounding control coil 46 is energized, and is capable of dropping under gravity to displace the mercury so as to close the circuit as shown in FIGURE 3. I

Thev plunger or core 45 can desirably be of an extremely thin spiral high silicon transformer sheet suitably wound in spiral form, contained within a completely surrounding jacket or copper sheath 47 which is suitably united at the ends as by brazing. The center of the core which is not magnetically very effective because of the space from the coil, is desirably filled with I a copper weight 48.

In an alternative form of the invention, the switch can be made to close when control current is applied and open when the control current is interrupted. This is accomplished, for instance, by eliminating enough of weight 43 so that the plunger 45' will float on the mercury when the control current is interrupted. in this embodiment, the control coil to is placed around the ceramic tube 35 so that when control current is applied, the plunger 45 is drawn into the mercury pool 4% and the mercury is displaced to the level of FIGURE 3 whereby the switch is closed. When the control current to coil as is interrupted, the plunger floats and the mercury level drops to the level 7 shown in FIGURE 1.

The entire switch is desirably potted as in epoxy resin or other suitable insulating adhesive to form an insulated supporting container 51. which extends out but not far enough to interfere with access to the terminal lugs. The epoxy resin suitable for this application is thoroughly described in the text Epoxy Resins: Their Applications and Technology, published in 1957 by H. Lee and K. Neville.

In placing the parts in position, the components comprising the' upper section are cemented together. This assembly is then cemented tothe lower assembly by immersion into the upper portion of liquid epoxy 51. 51 is composed of two separate pours of epoxy. The first pour of epoxy is up to approximately the horizontal center line of arm 3d. This is then permitted to dry. The second pour, used for sealing and finishing completes the casting i l. The top section is put into place with this second pour still liquid.

Where alternating current is to be used on the control coil 46, the entire upper section comprising the ceramic tube ll, copper tube 33, and the ceramic tube 43 is made of ceramic and the copper sheath surrounding the core 45' is desirably slit longitudinally at 52 and also beyond the center at each end as seen in FIGURE 6 so as to prevent excessive eddy current loss. This slit is then treated with a metallic spray 53 of molybdenum or other metal which does not readily reset with mercury so as to prevent mercury from bridging the gap and acting as a short circuit on the core when AC. is used on the coil.

In order to make an effective dash-pot action in case of magneto motive force which might burst the switch container or tend to separate the mercury completely, I provide a clearance of the order of 0.3 inch between the outside diameter of the core 45 and the inside diameter of the ceramic tube 4-3.

When this restricting action becomes effective, the core plunger is down and i elf causes electrical contact between two portions of mercury when separation would otherwise completely open the contact, as shown at FIG- URE 4.

It will be evident in the present invention, besides achieving the advantages of compactness, low cost and low heat loss, the invention is very well suited to use with high freque cy. The mercury layer which completes the circuit is in the form or" a ring annulus which is most ef fective in using high frequency. The ring is conveniently maintained in a vacuum or in a complete inert gas atmosphere, and the portion remote from the ring toward the center is utilized for a displacing device which performs the additional function of a throttling control device and also provides a low resistance contact in case-the mercury separates.

The device can be made to fail safe by closing the circuit and also rovide very eliective release. It will be evident that in case the magneto motive force was too violent to rel-ease through the throttling space between the core and the surrounding container wall, the increased flotation force would cause the core to rise and thus expend energy safely.

All of the parts should be assembled in a vacuum or in inert atmosphere wherein there will be a complete filling of gas inside.

areas a In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the beneiits of my invention without copying the structure shown, and 1, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a switch for electrical contact having an open and a closed position, an upper and lower tubular terminal longitudinally and vertically aligned and spaced, a leadin conductor connected to each of said terminals, electrical insulation in contact with and surrounding the terminals and forming with the terminals and conductors a cylinder closed at the bottom wherein the lower terminal forms the lower portion of said cylinder and the upper terminal forms the upper portion of said cylinder, mercury within the cylinder which extends to a level below the upper terminal when the switch is in an open position, and a longitudinally and vertically movable cylindrical plunger extending concentrically within the cylinder and spaced therefrom and which is adapted to extend above the mercury when the switch is in an open position, and to displace the mercury into the shape of a tube extending longitudinally in the space between the plunger and cylinder and into annular contact with the upper terminal, lower terminal, and plunger whereby a continuous concentric metallic tubular cross section is created between the lead-in conductors.

2. A switch of claim 1, in which said plumer is magnetically susceptible in combination with electromagnetic means for moving said plunger.

3. A switch of claim 1, wherein said plunger is gravity actuated to displace said mercury.

4. A switch of claim 1, wherein said plunger is electrically actuated to displace said mercury.

5. A switch of claim 1, in combination with means for maintaining an inert gas atmosphere around said switch.

6. A switch of claim 1, in combination with means for maintaining a vacuum around said switch.

7. A switch of claim 1, wherein said insulation comprises epoxy resin.

8. A switch of claim 1, in combination with throttling means whereby energy imparted to said mercury when the switch is in a closed position by an excess of current is dissipated.

9. A switch of claim 1, in combination with means for forming an electrical contact between terminals in the event of discontinuance of mercury contact between the terminals.

.10. A switch of claim 9, wherein the said means for forming an electrical contact between terminals comprises a copper sheet on the said plunger, a tubular mercury column between the lower terminal and the plunger, and a tubular column of mercury between the upper tubular terminal and plunger.

ll. A switch of claim 1, having a restricted mercury path between the upper terminal and the plunger, said switch being adapted to expend energy by hydraulic projection of mercury through the restricted path suppleented by vertical movement of the plunger in case of excessive current flow when the switch is in closed position.

References Cited in the file of this patent UNITED STATES PATENTS 375,403 Waterhouse Dec. 27, 1887 1,967,950 Larson July 24, 1934 2,649,890 Johnson June 2, 1953 2,988,778 l-luncilrer Apr. 18, 1961 

1. IN A SWITCH FOR ELECTRICAL CONTACT HAVING AN OPEN AND A CLOSED POSITION, AN UPPER AND LOWER TUBULAR TERMINAL LONGITUDINALLY AND VERTICALLY ALIGNED AND SPACED, A LEADIN CONDUCTOR CONNECTED TO EACH OF SAID TERMINALS, ELECTRICAL INSULATION IN CONTACT WITH AND SURROUNDING THE TERMINALS AND FORMING WITH THE TERMINALS AND CONDUCTORS A CYLINDER CLOSED AT THE BOTTOM WHEREIN THE LOWER TERMINAL FORMS THE LOWER PORTION OF SAID CYLINDER AND THE UPPER TERMINAL FORMS THE UPPER PORTION OF SAID CYLINDER, MERCURY WITHIN THE CYLINDER WHICH EXTENDS TO A LEVEL BELOW THE UPPER TERMINAL WHEN THE SWITCH IS IN AN OPEN POSITION, AND A LONGITUDINALLY AND VERTICALLY MOVABLE CYLINDRICAL PLUNGER EXTENDING CONCENTRICALLY WITHIN THE CYLINDER AND SPACED THEREFROM AND WHICH IS ADAPTED TO EXTEND ABOVE THE MERCURY WHEN THE SWITCH IS IN AN OPEN POSITION, AND TO DISPLACE THE MERCURY INTO THE SHAPE OF A TUBE EXTENDING LONGITUDINALLY IN THE SPACE BETWEEN THE PLUNGER AND CYLINDER AND INTO ANNULAR CONTACT WITH THE UPPER TERMINAL, LOWER TERMINAL, AND PLUNGER WHEREBY A CONTINUOUS CONCENTRIC METALLIC TUBULAR CROSS SECTION IS CREATED BETWEEN THE LEAD-IN CONDUCTORS. 